Telephone call metering



June 13, 1961 H. TPFr-:R ET AL 2,988,600

TELEPHONE CALL METERING Filed May 2o, 1955 D U N United States Patent l,

y fmLEPHoN-E CALL METERlNG Herbert Tpfer, Munich, and Friedrich Plleiderer M- nichisolln,cerrnany, "gnors to siemens & Ilalske Aktiengesellschaft, Munich and Berlin, Germany, a

corporation of GermanyV Filed May Y20, 1955, Set. ANo. 509,998 In Germany July 25, 1949 Public Law 619, Aug. 23, `1954 Patent expires July` 25,. ,19.69 -2 Claims. (Cl. 179-71) This invention relates to telephone call :metering fand is particularly concerned with a circuit arrangement tor 'metering Calls y21Itf'lCl'lg O ill fald/ '01 VZlle JIijflilnient/s.

The switching signals required vfoi building up calls `rover *two-conductor 'trunk lines 'are in the system assumed in connection with the invention transmitted with *alternatingcurrent with a frequency, for example, of 5o cycles. 'The line conductors are 'during Iconversation between part-ies exclusively used for the talking curr-ents, the tr-ansmission of the switching 'signals for eifecting 'seizure of switching devices and number selection being 'eire'cted prior to switching calls through, and signals for the release of connections and for the call metering being transmitted responsive Ito conclusion of calls. v

-vIt call metering is desired during the time calls are Vlin progress, 'Wh-ich `results in `considerable advantages Vso A'fa'- 'as the expenditures for switching means for the call metering devices and the utilization of high-'grade trunks are concerned, 'care must be taken to avoid disturbance `of the talking parties by metering impulses transmitted over trunk lines.

A'Proposals have been made 'to use in such cases direct current impul'sse for (effecting the metering. However, 'the :corresponding arrangements necessitate changes 'in the 'repeaters at the ends 'of trunk lines and connecting thereto direct current potentials, such vchanges making the aclvantage of repeaters questionable.

A further possibility is to transmit metering impulses vwith alternating current, `simultaneously over the corresponding line conductors of trunk lines. 'Such transmission 'rnay be carried out without 'disturbing existing calls, but it prevents utilization of trunks in phantom circuits for -a -plurality of 'simultaneous connections.

The invention proposes to transmit over 'trunk Ilines alternating current metering impulses which are .periodically effective in different time sequence according to Azones involved, while a call is in progress, in the saine manner as the alternating current impulses used for switching signals for the building up of the corresponding connection, `and preferably with the same frequency, for example, 25 or y50 cycles.

In order to 'avoid disturbing existing Vcalls over the corresponding trunk line, care must be taken in such -surprisin'gly simple arrangement to prevent passage o`f 'the alternating current metering impulses in the direction of the exchange by the provision of high pass filters at the trunk 'line ends, and to clear the transmitted Vfrequency of higher frequencies by the provision of a low pass filter at the transmission point, which is, in the assumed case, at the outgoing end of the trunk line.

The advantage of the arrangement according to the invention resides above all in the fact that the devices for the periodic metering need not be disposed in subexchanges but can be transferred to central exchanges of higher order. Since the number of subexchanges exceeds that of the central exchanges by several times, there will result a considerable reduction of costly switching devices such as timers and zone switches.

The foregoing and other objects and features will ap- Patented June 13, 1961 lCe pear -frorn lthe description rendered below with reference to fthe accompanying -liagra1rrlatic 'rawin`g`, Whoeih FIG. lv-shows fan embodiment ofthe invention, illus- 't-rjatig Ionly the details required for an understanding thereof; n

lFIG. l2 indicates a choke coil Iused in the system v'of l; and l 3 is a curve to explain the nature ofthe core material for vthe "choke coil.

There is Aprovided two-conductor trunk 1lille Which iis inclut-:tively blocked atv'e'ach end by repeaters connected thereto Over this line are -built up connections, automatically, in known marmer, 'extending i lthe direction of the arrow, by transmitting alternating current in the ytnitgoing repeater Ufk, such signals are received by l'the impulse relay lfb which retransmits thern Ain 'usual manner, las ground impulses, over 'the 'upper trunk conductor, by actuation of contact jb, jfor the 'purpose of setting the successive 'switching devices. The 'transmission of alternating current switching sign` ls and retransmission 'of Corresp'ondin'g direct `current impulses is repeated until the connector is -nally 'set viii-th its wipers iin engarge'rnent with Ythe bank contacts of the called line.

When the called party answers, the relay `G 'in the outgoing 'repeater Uk will be energized by an impulse transinitted from the connector (not shown), lUpon energizing, relay G disconnects Ithe impulse relay Ib by opening contact g2., and Vcloses iits contact gl to start a 'timer which causes periodic energi-Zation of the relay Relay Z connects at its ycontact z periodically alternating `ncurrent, preferably 50 cycles, from the source fQf=`50, for transmission over the trunk line The metering impulses thus transmitted over the vtrunk line VL by way or repeaters Uk and Ue reach `the meter 'control relay l in 'the incoming repeater Ua, and such relay retransmits Athese impulses at its contact z' to the meter Zr of the calling parity.

The connection fof the alternating current metering impulsesfrom 'the transmitting 'point to the trunk line iis effected in fthe same manner as the 'connection of zthe alternating current signals for 'building up 'a call. The alternating current metering impulses accordingly llowli'n Aeach ioase over the serially disposed windings of .the repea'ters.

In order to prevent passage of the alternating metering vcurrent pulses to exchange portions of the corresponding connection, there is a high pass iilter HF `provided in the repeater at each end of the trunk line VL. These high pass "lilt'ers block the metering frequency but ,pass the speech frequencies. Moreover, in order lto avoid dis- Vtui-hingfauexi'sting call lby the metering frequency, there is Yprovided a loW pass `filter between the current source Q=5O and the line conductors of the outgoing repeater Uk, such low pass lter being effective to clear the transmitted frequency of higher frequencies, especially incident to switching operations. It is of decisive importance for this lter circuit that the core of the coil Sp disposed nearest to the line conductors (talking cirzuit) is made of a material which exhibits a permeability that remains substantially constant over a predetermined range of the alternating current which aifects the eld strength thereof, examples of which are disclosed in publication entitled Gecalloy Low Loss Cores Micropowder Magne Coils of this type are well known, for exwhich the magnetization curve becomes flatter. computation of the inductivity, the presence of an air gap results in the necessity of increasing the number of Vmeability factor. alternating current approximately linear; the saturation -induction is not obtained at maximum operating current. ISuch curves may be obtained with various core material.

trated in German reference Lehrbuch fuer Funkempfangstechnik, by H. Pitsch, copr. 1948 by Akademische Verlagsanstalt Geest & Portig K.G., Leipzig, pages 64- 65, Section 403 Eimluss des Luftspaltes bei Transformatoren und Drosseln, English translation of which brought out in the last-mentioned article, there is always -an optimum air gap length, corresponding to the highest possible inductivity, above which optimum, or below In the turns in order to compensate for the inductivity decrease due to the lower total permeability, and the iron crosssection must be decreased in order to prevent a decrease in the line density. In practice, the number of turns and the iron cross-section are increased, since larger numbers `of windings generally must be mounted on a larger core.

Consequently, the magnetization curve and thus the in- .ductive impedance of the choke may be made relatively linear by proper dimensioning and corelation of the air gap, winding turns, core cross-section for optimum results.

Nonlinear distortions and therewith higher frequencies are in this manner avoided in the output circuit of the filter; metering impulses reach the trunk line with a suficiently pure sinusoidal curve form.

As shown in FIG. 2, the two windings of the choke coil are disposed upon a circular or rectangular core provided with an air gap.

FIG. 3 indicates the magnetization curve of the core of the choke coil, letter H indicating the electric field strength, B the magnetization induction and fr the per- The curve .is in the range of the Highly alloyed sheet material with low hysteresis and eddy current losses may be used. An air gap may be provided if desired so as to improve the linearity of the magnetization curve.

In order to exclude any disturbance of the call in progress, the transmitted metering frequency is `furthermore connected to the line conductors of the repeater Uk at the outgoing end of the trunk line over a resistor Wi which is fixedly disposed in the corresponding transmitting circuit. The permanent presence of this high resistance resistor results in a low residual current flowing over the lter TF whereby switching surges are in much better way avoided than would be the case with complete disconnection of the metering current source from the trunk line.

may be found in the library, U.S. IPatent Office. As

of the magnetic core material similar to that for the chope coil Sp, that the magnetic conductivity of the relay core suffers, incident to attraction of the armature responsive to the metering impulses, no changes that may disturb the existing call by current distortions caused thereby and in turn causing repercussions such as clicking noise in the talking circuit. A filter chain ahead of the corresponding relay may in this manner be dispensed with.

Changes may be made within the scope and spirit of the appended claims.

We claim:

1. In a telephone system having a two-conductor trunk line including a repeater connected thereto respectively at the incoming and at the outgoing end thereof, over which trunk line calls are extended from calling to called stations by transmitting thereover switching signals in the form of alternating current impulses of predetermined frequency, a device for metering a call extended over said trunk line, while such call is in progress, by periodically transmitting over said trunk line metering current in the form of alternating current impulses at a frequency corresponding to that of said switching signals, said device comprising an alternating current source for producing said vmetering current, choke coils forming a filter circuit connected to the repeater at the outgoing end of said trunk line, means including a high ohmic resistor for connecting said alternating current source to said filter circuit, said resistor normally causing a current flow of low magnitude from said current source over said filter circuit to said outgoing repeater, and means for periodically short-circuiting said resistor to transmit the alternating metering impulses to the outgoing repeater, for transmission thereof over said trunk line, said filter circuit being operative to filter from said metering current frequencies exceeding a rated frequency, one of said choke coils of said filter circuit which is disposed nearest to said outgoing repeater comprising a core made of a material having a permeability which remains substantially constant over a predetermined range of the operating alternating current affecting the field strength thereof.

2. A system and cooperation of parts according to claim 1, comprising a meter control relay disposed in the repeater connected tothe incoming end of said trunk line, said meter control relay receiving the alternating current metering impulses transmitted over said trunk line and operatively responding thereto by attraction of its armature to effect operative actuation of a metering circuit for registering said impulses and thereby metering the corresponding call, said meter control relay comprising a core made of a magnetizable material the magnetic conductivity of which remains substantially unaltered responsive to attraction of the armature.

References Cited in the le of this patent UNITED STATES PATENTS 1,723,153 Green Aug. 6, 1929 1,834,393 Fowler Dec. 1, 1931 2,218,571 Beale Oct. 22, 1940 2,282,911 Topfer et al. May 12, 1942 

